It is not an optimal combination but I thought I would throw in my thoughts and recommendations, and explain what I personally look for in multiclassing.
I'm going to start by saying that the order does not matter beyond the first level in this scenario and should progress according to your characters background. Unless you are multiclassing fighter to align the feat pre-requisite with the bonus feat every 3 levels, you should not worry about progressing to level 9, but rather what your end goal is, and which is most optimal to take after level 9.
From a game mechanic perspective, how should I multiclass a Bard/Sorc to level 9, in order to "get the most out of each class"? That is, receiving high utility from the class characteristics, while also achieving a sense of natural progression within the scope of the character (as described above).
If we divide all the classes into three subclasses (fighter, caster, utility) for multiclassing purposes your first level generally prioritizes in this order: Utility -> Fighter -> Caster. So in this scenario, the Bard falls under utility, both optimal and story wise it makes sense to start with bard. Here are the numbers:
The Bard provides: 6hp, (6+i)x4 skill points
The Sorc provides: 4hp, (2+i)x4 skill points
Sorcerer:
The sorcerer gains access to higher spells every 2 levels starting at level 2 with the exception of level 1. (1 level after a wizard obtains their spells except they share the first level at level 1). For spells, you best levels will be 1st, 4th, 6th, 8th.
Your sorcerer BAB progresses at .5 (there are 3 categories, you either have a 1:1 level to BAB ratio = Fighter, a 1:.75 = Utiltiy, or a 1:.5 = Caster) which means that every other level starting at level 2 is optimal for BAB: 2nd, 4th, 6th, 8th.
Your sorcerer saves progress at .3/.3/.6 which means every 3 levels your Fort and Ref will increase by 1. Every 2 levels starting at level 2 your Will shall progress. Optimal levels for saves are: 1st, 3rd, 6th, 9th.
Spells Known: 0-level increase every other level starting at level 2, 1st-level spells progress every other level starting at level 1, and additional spells progress at every other level starting at the 4th level and every even level after that. Optimal spells known will be every odd level starting at 5th, and will be better the more levels you invest in sorcerer.
Special: Sorcerers gain a familiar at level 1
Bard:
Your bard spells progress every 3 levels with the offset of the second level gaining the first level 1 spell. Your spells per day will influence this so we will count the 0 spells per day as the optimal level: 2nd, 4th, 6th, 8th.
Your BAB progresses as a ulitity character (.75 of your level) and due to the way the game rounds, we will only mention the bad levels: 1st, 5th, 9th.
Finally your saves progress at .3/.6/.6 thus you will have the same Fort and Will as a sorcerer, the exception is a higher reflex. Thus the optimal bard levels are: 1st, 4th, 6th, 8th.
Special: Bards gain special abilities at: 1st, 3rd, 6th, and 8th levels.
Conclusion
I am going to take the most occurring optimal level in each class, compare it against the remaining levels in the opposite class, and list a few combinations below with their stats: (This assumes HP will be at 1/2 dice roll + 1. So 6hd = 4hp, 4hd = 3hp)
8 Bard, 1 Sorc: (recommended)
HP: 37(34bard,3sorc)
BAB: +6/+1
Fort/Ref/Will: 2/6/8
Spells: (spell level - class : number)
0-Sorc: 5 | 1-Sorc: 3 | 0-Bard: 3 | 1-Bard: 3 | 2-Bard: 3 | 3-Bard: 1
Skills: (6 + i) * 11 + 2 + i
6 Bard, 3 Sorc:
HP: 35(26bard,9sorc)
BAB: +5
Fort/Ref/Will: 3/6/8
Spells: (spell level - class : number)
0-Sorc: 6 | 1-Sorc: 5 | 0-Bard: 3 | 1-Bard: 3 | 2-bard: 2
Skills: (6 + i) * 9 + (2 + i) * 3
3 Bard, 6 Sorc:
HP: 32(14bard,18sorc)
BAB: +5
Fort/Ref/Will: 3/5/8
Spells: (spell level - class : number)
0-Sorc: 6 | 1-Sorc: 6 | 2-Sorc: 5 | 3-Sorc: 3 | 0-Bard: 3 | 1-Bard: 1
Skills: (6 + i) * 6 + (2 + i) * 6
Sub questions:
Which class should be the starting class, and why?
How should I progress to level 9? Which dips should I make and when?
What good feat combinations can me made? Same for skills and spells?
Is there a race that would be particualarly beneficial for this combo?
1) The starting class would be bard, because the only unique boons that come from first level are skills and hit dice.
2) Progress to level 9 however you like, with this combination there is nothing special you can gain by taking the levels in a specific order. An example of a scenario where leveling order matters: 12Fighter/6Ranger/2Monk, taking your 12th level of Fighter @ level 18 so that you can spend both your free feat AND your fighter feat on say, Greater Weapon Specialization (Bow, Unarmed Strike)
3) I cannot recommend feats because there are so many ways that you can build a character, this is based around your preference and how you wish to handle combat situations. I also do not multiclass casters because you rarely stray from the caster path when you do so. Lastly, I do not play casters enough to give a strong feat recommendation.
4) Skills and Spells should revolve around what your party needs. Bard is more crowd-control and disable orientated. The sorcerer will be your damage output. Both classes can provide buffs. High charisma will go into your save DC's and that will benefit the Bard over the Sorcerer. Some of my personal favorite spells: Grease, Haste, Heroism. Again it revolves around your party role and play style.
5) Your primary stats will be Charisma with Con as a most likely second choice, dexterity is good, however you would have to invest a lot into it to make it work for ac, by that time you will be getting hit anyway in combat = health is more viable. Strength will most likely be your dump stats, and with both the Bard and Sorc having high Will saves and high skills, you could dump-stat Wisdom. Never take a bonus to a dump stat, especially in 3.5. The higher the stat, the greater the point-buy value you will get from it.
1st Gnome: +2 con is a stat we are looking for, and the -2 str is a stat we are looking to dump.
2nd Hafling: +2 dex is another stat we are okay with having, and it also shares the same dump stat. Like the gnome, the size bonus will compliment the caster/utility build.
3rd Human, Half-elf: For multiclassing these two races are never bad.
If you provide more information, such as starting stats (point buy?) or if there are any book restrictions, or alternative classes you are considering taking I can look more into it for you.